1. Field of the Invention
This invention lies in the field of electronic time range expanders, such as might be used in connection with the display or recording of sonar signals. Still more particularly it concerns an expander in which the time rate of sequential output values of the sonar receiver are timed at one-half their normal time rate so that the time and depth scale is thereby expanded.
2. Description of the Prior Art
Most sonars which display returned echoes versus time (distance) use a motor driven mechanism to move a lamp around a disc or a stylus across electrosensitive chart paper to give the time (distance) dimension. The faster the mechanism runs, the more the scale is expanded. For instance, doubling the speed of a rotating disc from 40 revolutions per second to 80 revolutions per second will change the scale from 0-60 feet to 0-30 feet expanding (making longer) all received signals.
There is a practical limit to how fast a scan disc can be turned, or a stylus can be driven across the chart paper. As the speed increases, it becomes more susceptible to reliability and wear problems because stress increases on the mechanism. A number of means have been developed to expand the sonar information without increasing the speed of the mechanism. They all involve digitizing the detected sonar signal, storing it in a random access memory or shift register, and later sending it out serially at a slower rate. All of these ways involve a lot of circuitry and delay of the display of the sonar signal until the memory or shift register has been filled. These circuits also cannot be retrofitted into sonars not specifically designed to take them.
This invention utilizes a circuit that has fewer components, does not delay the display of the sonar signal, and is retrofitable into any sonar by simply placing it in series with the signal line to the display driver.